The present invention generally relates to energy storage systems for hybrid electric vehicles, and, more particularly, to a system and method for balancing the state of charge of energy storage modules in a hybrid electric vehicle.
Over the past few years, there has been a growing concern over global climate change due to an increase in carbon dioxide levels as well as oil supply shortages. As a result, some automobile manufactures and consumers are beginning to have a greater interest in motor vehicles having low emissions and greater fuel efficiency. One viable option is a hybrid electric vehicle (HEV) which allows the vehicle to be driven by an electric motor, combustion engine, or a combination of the two.
Though various features are important to the overall HEV design, the system which stores the energy available for use by the vehicle is a key component. The energy storage system is provided within the HEV to store the energy created by a generator in order for that energy to be available for use by the hybrid system at some later time. For example, the stored energy may be used to drive an electric motor to independently propel the motor vehicle or assist the combustion engine, thereby reducing gasoline consumption.
However, energy storage systems face a variety of design complications. One of the major concerns during operation is maintaining a proper balance between the packs with respect to the state of charge (SOC) of individual packs in a multi-pack energy storage system. It is important that the individual packs are maintained at a SOC within a certain tolerance with respect to one another. If the difference in SOC between packs exceeds the tolerance, damage to the vehicle's electrical components can occur.
Prior art systems have thus far achieved pack or cell balancing with complicated hardware and circuitry which suffers from various drawbacks, such as inefficiency, increased cost, and increased risk of failure. In addition, prior systems have focused on transferring charge between packs, which results in energy loss due to the inefficiency of the transfer process.
Thus, there is a need for improvement in this field.